1. Field of the Invention
The present invention relates to a probe for an ultrasonic endoscope which observes an object inside a body cavity by using an ultrasonic wave, and relates to an ultrasonic endoscope system, an ultrasonic observation system and an ultrasonic video endoscope system, all of which utilize the probe mentioned above.
2. Related Art Statement
An ultrasonic endoscope system utilizing a probe has been known for example from Japanese Patent Laid-Open Publication No. 57-190,552, wherein an object inside the body cavity is diagnosed with an ultrasonic wave by rotating mechanically an ultrasonic vibrating element arranged in a distal end of an insertion section of the probe by means of a driving member arranged apart from the insertion section.
FIG. 1 is a schematic view showing an embodiment of the probe disclosed in the Japanese Patent Laid-Open Publication No. 57-190,552. In this embodiment, A is the insertion section and B is the driving member.
In a distal end of the insertion section A, an ultrasonic vibrating element 1 is rotatably secured by means of a bearing 2, and a tip portion of a flexible shaft 3 is connected to the ultrasonic vibrating element 1. The flexible shaft 3 is held in a flexible outer tube 5 through a liquid paraffin 4 and a proximal end of the flexible shaft 3 is introduced to the driving member B.
The driving member B comprises an electric motor 6 as a driving means, a gear box 7 for decelerating a rotation speed of the electric motor 6, an output shaft 8 including a shaft member 8a and a bearing 8b, for transmitting the decelerated rotation to the flexible shaft 3, and a potentiometer 9 arranged to the electric motor 6.
The prior art ultrasonic endoscope system mentioned above has drawbacks mentioned below. In the case that a patient swallows the insertion section A of the probe, it is a matter of course that the patient can easily swallow the insertion section A if it is thin. However, if the flexible shaft 3 is made thinner so as to make the insertion section A thin, kinks are liable to occur on the flexible shaft 3, and thus the rotation of the electric motor 6 is not transmitted accurately. That is to say, if the above kinks are generated, the rotation of the ultrasonic vibrating element 1 is decreased correspondingly, and thus if an amount of kinks reaches to a predetermined level, the rotation of the ultrasonic vibrating element 1 is increased over a normal rotation level. As a result, a time-angle characteristic of the rotation of the ultrasonic vibrating element 1 is vibrated as shown in FIG. 2 by a solid line. Moreover, characteristics during respective scanning periods T1, T2 . . . are varied one another. Therefore, as shown in FIG. 3 by a solid line M and a dotted line N, the clinical image obtained by the known ultrasonic endoscope system becomes large or small with respect to the normal one, and thus an accurate diagnosis is not realized.
Further, as clearly understood from FIG. 2, since the time-angle characteristic is varied pulsatory as shown by a solid line with respect to the normal linear variation as shown by a dotted line and this pulsatory variation occurs irregularly, a starting point of the next scanning operation is varied. As a result, the obtained image position is varied correspondingly, For example, this variation becomes at a rate of .DELTA..theta.=20.degree., and thus accurate diagnosis cannot be achieved.
To eliminate the distortion and the positional variation in the clinical image, if the flexible shaft 3 is made thick and stiff, the following disadvantages occur. If the flexible shaft 3 is made thick and stiff, the kinks remain on the shaft 3 because it is normally long. Therefore, the rotation of the motor 6 becomes somewhat stable, but the scanning characteristic of the ultrasonic vibrating element 1 is not linear but still pulsatory. Moreover, in this case, since the insertion section A becomes large and stiff (not flexible), the patient does not swallow the insertion section A easily and an operationability of the insertion section A in the body cavity becomes bad.
Contrary to this, since use is made of a D.C. motor as the electric motor 6, so-called brush noise is generated on a signal line of the ultrasonic vibrating element 1. As a result, a flicker effect is generated on an image displayed on a CRT by a scanning operation of the ultrasonic vibrating element 1. This flicker effect can be eliminated by a noise reduction circuit such as a filter. However, in this case, since it is necessary to arrange a specific noise reduction circuit, the ultrasonic endoscope system becomes large and complicated, and further a reliability becomes low.
Further, in the known ultrasonic endoscope system, since use is made of the electric motor which is large in size and complicated in mechanism, there is a drawback that the operationability thereof becomes bad.